Method for manufacturing compound semiconductor epitaxial substrate

ABSTRACT

A method for manufacturing a compound semiconductor epitaxial substrate with few concave defects is provided. The method for manufacturing a compound semiconductor epitaxial substrate comprises a step of epitaxially growing an InGaAs layer on an InP single crystal substrate or on an epitaxial layer lattice-matched to the InP single crystal substrate under conditions of ratio of V/ : 10-100, growth temperature: 630° C.-700° C., and growth rate: 0.6 μm/h-2 μm/h.

TECHNICAL FIELD

The present invention relates to a method for manufacturing a compoundsemiconductor epitaxial substrate. More specifically, the inventionrelates to a method for manufacturing a compound semiconductor epitaxialsubstrate with few concave defects.

BACKGROUND ART

When an epitaxial layer has been grown on a single crystal substrate byconventional vapor phase epitaxy, in particular, metal-organic chemicalvapor deposition (MOCVD), convex defects or concave defects havesometimes generated on or in a surface of the epitaxial layer.

Convex defects are called tear-drop-like defects or hillocks; theirdiameters are 10 μm to 30 μm and their heights are several tens ofnanometers. Despite the convex defects, semiconductor devices can bemanufactured, but in some cases, the defects have damaged photo masksused in their manufacturing process or have caused displacements ofpatterns. Therefore, to reduce convex defects, a method of controllingoff-angle of single crystal substrate have been proposed (for example,JP-A-2-239188 and JP-A-8-78348).

On the other hand, concave defects have diameters of several micrometersand depth reaching the vicinity of an interface between a single crystalsubstrate and an epitaxial layer. When a semiconductor device ismanufactured by using a compound semiconductor epitaxial substrate withconcave defects, the semiconductor device yield decreases.

Besides, it has been difficult to reduce the concave defects through theuse of the method for reducing the convex defects.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a method formanufacturing a compound semiconductor epitaxial substrate with fewconcave defects.

The present inventors conducted extensive studies to reduce the concavedefects, and resultantly completed the invention.

That is, the present invention provides a method for manufacturing acompound semiconductor epitaxial substrate comprising a step ofepitaxially growing an InGaAs layer on an. InP single crystal substrateor on an epitaxial layer lattice-matched to the InP single crystalsubstrate under conditions of

-   -   ratio of V/        : 10-100,    -   growth temperature: 630° C.-700° C. and    -   growth rate: 0.6 μm/h-2 μm/h.

Further, the present invention provides a method for reducing concavedefects in a compound semiconductor epitaxial substrate comprising astep of epitaxially growing an InGaAs layer on an InP single crystalsubstrate or on an epitaxial layer lattice-matched to the InP singlecrystal substrate under conditions of

-   -   ratio of V/        : 10-100,    -   growth temperature: 630° C.-700° C. and    -   growth rate: 0.6 μm/h-2 μm/h.

Furthermore, the present invention provides a compound semiconductorepitaxial substrate obtained by using the above manufacturing method.

EFFECT OF THE INVENTION

According to the method for manufacturing a compound semiconductorepitaxial substrate of the present invention, a compound semiconductorepitaxial substrate with few concave defects is obtained.

Also, according to the method of the present invention, it is possibleto reduce concave defects in a compound semiconductor epitaxialsubstrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of a compound semiconductorepitaxial substrate obtained by using the manufacturing method accordingto the present invention.

FIG. 2 shows a cross-sectional view of a compound semiconductorepitaxial substrate obtained in Example 1.

FIG. 3 is a photograph of a surface of the compound semiconductorepitaxial substrate obtained in Example 1.

FIG. 4 shows an indium distribution within an InGaAs layer included inthe compound semiconductor epitaxial substrate obtained in Example 1.

FIG. 5 shows an indium distribution within an InGaAs layer included in acompound semiconductor epitaxial substrate obtained in Example 2.

FIG. 6 is a photograph of a surface of a compound semiconductorepitaxial substrate obtained in Comparative example 2.

FIG. 7 shows a relationship between growth temperature of InGaAs layerand surface defect density of compound semiconductor epitaxial substrateobtained.

FIG. 8 shows a relationship between growth rate of InGaAs layer andsurface defect density of compound semiconductor epitaxial substrateobtained.

FIG. 9 shows a relationship between V/

ratio of grown InGaAs layer and surface defect density of compoundsemiconductor epitaxial substrate obtained.

BEST MODE FOR CARRYING OUT THE INVENTION

Method for Manufacturing Compound Semiconductor Epitaxial Substrate

A method for manufacturing a compound semiconductor epitaxial substrateaccording to the present invention is illustrated with reference toFIG. 1. FIG. 1 is a cross-sectional view of a compound semiconductorepitaxial substrate (hereinafter abbreviated as “epitaxial substrate”) 1obtained by using the above manufacturing method. The epitaxialsubstrate 1 includes an InP substrate 2, an optional InP layer 3, anInGaAs layer 4, and an optional InP layer 5 in this order.

The InP substrate 2 is, for example, a single crystal substrate with anoff-angle, which is a deviation from a plane direction (100), of aboutnot more than 5°, preferably not more than 0.5°. The InP substrate 2 ispreferably a substrate with an off-angle of about 0° (just substrate) inviewpoint of controlling the amount of impurities entrapped into theepitaxial layer and of applications in semiconductor lasers. Further,The InP substrate 2 has preferably the plane direction accuracy of±0.05° in the (100). A layer (for example, the InP layer 3 shown inFIG. 1) being lattice-matched to the InP substrate 2 is preferably grownon the InP substrate 2. Examples of the epitaxial layer beinglattice-matched to the InP substrate 2 include an InP layer, InGaAslayer, InAlAs layer, InGaAsP layer, and GaAsSb layer. The layer beinglattice-matched to the InP substrate 2 may be grown by vapor growth suchas MOCVD and molecular beam epitaxy (hereinafter referred to as MBE).The vapor growth of the InP substrate 2 may be carried out underconventional conditions.

The InGaAs layer 4 is grown on the InP substrate 2, or on an optionalepitaxial layer grown on InP substrate 2 which is lattice-matched to theInP substrate 2. The InGaAs layer 4 may be grown by vapor growth such asMOCVD and MBE, preferably grown by MOCVD.

The ratio of V/

in the vapor growth of the InGaAs layer 4 is not less than 10,preferably not less than 50 and is not more than 100, preferably notmore than 70. When the ratio of V/

is within the above range, an epitaxial substrate with few concavedefects is obtained. When the ratio of V/

is lower than 10, group V vacancy defects generate in the epitaxiallayer or anti-site defects (phenomena in which the group

elements occupy group V sites) generate. It is assumed that the group Vvacancy defect is related to shortage of the group V elements. The ratioof V/

means a proportion of feed rate of group V raw material to feed rate ofgroup m raw material for the manufacture of the

-V group epitaxial substrate. For example, in vapor growth, an organicmetal used as a raw material is fed in gaseous form from a gas cylinderor a bubbler.

When the gas cylinder is used, a feed rate of a raw material gas may becontrolled by using a flow controller such as a MASSFLOW placed on afeed line. The feed rate of raw material gas is represented as“concentration of raw material gas in the gas cylinder”×“flow rate ofraw material gas”.

When the bubbler is used, the feed rate of the raw material gas may becontrolled by using a flow controller such as a MASSFLOW placed on afeed which supplies a carrier gas to the bubbler. The feed rate of rawmaterial gas is represented as “flow rate of carrier gas”×“vaporpressure of raw material in bubbler”/“gas pressure in the bubbler”.

Examples of the group V raw material include arsine (AsH₃). Examples ofthe group

raw material include indium compounds such as trimethyl indium (TMIn),gallium compounds such as trimethyl gallium (TMGa) and triethyl gallium(TEGa). The gallium compound is preferably TMGa. By using TMGa, anepitaxial substrate including an epitaxial layer with uniformdistribution of indium (In) is obtained. A vapor growth temperature ofthe InGaAs layer 4 is not less than 630° C., preferably not less than640° C., more preferably not less than 650° C. and not more than 700°C., preferably not more than 680° C., more preferably not more than 670°C. When the vapor growth temperature is within the above range, anepitaxial substrate with few concave defects is obtained.

A vapor growth rate of the InGaAs layer 4 is not less than 0.6 μm/h,preferably not less than 0.8 μm/h and not more than 2 μm/h, preferablynot more than 1.2 μm/h. The vapor growth rate may be controlled byadjusting the feed rate of raw material gas.

In the method for manufacturing a compound semiconductor epitaxialsubstrate according to the present invention, further, a layer may befurther grown on the InGaAs layer 4. For example, a InP layer 5 may begrown thereon. The InP layer 5 may be grown by vapor growth such asMOCVD and MBE.

Method of Reducing Concave Defects in Compound Semiconductor EpitaxialSubstrate

In the method of reducing concave defects in a compound semiconductorepitaxial substrate according to the present invention, the concavedefects is reduced by growing an InGaAs layer on a single crystal InPsubstrate by vapor growth such as MOCVD and MBE under the sameconditions as described above (ratio of V/

, temperature, growth rate, In raw material, Ga raw material and As rawmaterial). The single crystal InP substrate may have an off-angle ofabout not more than 5°, preferably not more than 0.5°.

Compound Semiconductor Epitaxial Substrate

A compound semiconductor epitaxial substrate according to the presentinvention includes, for example, an InP substrate 2, an optional InPlayer 3, an InGaAs layer 4, and an optional InP layer 5 in this order asshown in FIG. 1.

The InP substrate 2 has a thickness of not less than about 250 μm andnot more than about 700 μm. In the epitaxial substrate including the InPlayer 3, the InP layer 3 has a thickness of not less than about 0 μm andnot more than about 3 μm. The InGaAs layer 4 has a thickness of not lessthan about 0.1 μm and not more than about 6 μm and an In content of notless than about 0.51, preferably not less than about 0.52 and not morethan about 0.53. Further, in the epitaxial substrate including the InPlayer 5, the InP layer 5 has a thickness of not less than 0 μm and notmore than 2 μm.

The compound semiconductor epitaxial substrate is obtained by using theabove method for manufacturing a compound semiconductor epitaxialsubstrate.

EXAMPLES

The following examples will illustrate the present invention more indetail, but do not limit the scope of the invention.

Example 1

A compound semiconductor epitaxial substrate 1′ which has a layerstructure shown in FIG. 2 and is used for the manufacture of a p-i-ndiode, was obtained by using the following method.

An InP substrate 2′, which is a just substrate with a plane direction(100) and has a plane direction accuracy within ±0.05° and a diameter ofabout 8 cm, was placed in a MOCVD reactor for growing thin film.

The InP substrate 2′ was surface-treated by elevating a temperature inthe reactor to 660° C. and feeding a PH₃ gas. InP layer 3′ having athickness of 1 μm was grown on the InP substrate 2′ using TMIn as a rawmaterial. Then the PH₃ gas was changed for an AsH₃ gas, an InGaAs layer4′ having a thickness of 3 μm was grown under conditions of

-   -   raw material: TMIn and TEGa,    -   ratio of V/        : 70,    -   growth temperature: 660° C., and    -   growth rate: 1 μm/h.        The AsH₃ gas was changed for the PH₃ gas, an InP layer 5′ having        a thickness of 1 μm was grown.

The epitaxial substrate had a good surface quality of the InP layer 5′and no concave defects on the surface. A photograph of the surface wasshown in FIG. 3. The surface was observed by using a differentialinterference microscope. The In distribution in the InGaAs layer 4 ofthe epitaxial substrate obtained was shown in FIG. 4. In FIG. 4, alongitudinal axis indicated indium content(unit: %). The indiumdistribution was measured by using a high-resolution X-ray microanalyzer.

Example 2

An epitaxial substrate was obtained by the same operation as in Example1 except that TEGa was changed for TMGa as the Ga raw material forgrowing the InGaAs layer 4.

The epitaxial substrate had a good surface quality and no concavedefects on the surface. The indium distribution in the InGaAs layer 4was shown in FIG. 5.

Example 3

An epitaxial substrate was obtained by the same operation as in Example2 except that the conditions for growing the InGaAs layer 4 was changedfor the following.

-   -   ratio of V/        : 20,    -   growth temperature: 690° C., and    -   growth rate: 2 μm/h.

The epitaxial substrate had a good surface quality and no concavedefects on the surface.

Comparative Example 1

An epitaxial substrate was obtained by the same operation as in Example1 except that the conditions for growing the InGaAs layer 4 was changedfor the following.

-   -   ratio of V/        : 70,    -   growth temperature: 620° C., and    -   growth rate: 1 μm/h.

The epitaxial substrate had no good surface quality and many concavedefects on the surface.

Comparative Example 2

An epitaxial substrate was obtained by the same operation as in Example1 except that the conditions for growing the InGaAs layer 4 was changedfor the following.

-   -   ratio of V/        : 70,    -   growth temperature: 660° C., and    -   growth rate: 3 μm/h.

The epitaxial substrate had no good surface quality and many concavedefects on the surface. A photograph of the surface was shown in FIG. 6.

Comparative Example 3

An epitaxial substrate was obtained by the same operation as in Example2 except that the conditions for growing the InGaAs layer 4 was changedfor the following.

-   -   ratio of V/        : 120,    -   growth temperature: 660° C., and    -   growth rate: 1 μm/h.

The epitaxial substrate had no good surface quality and many concavedefects on the surface.

Test Example 1

An InP substrate 2′, which is a just substrate with a plane direction(100) and has a plane direction accuracy within ±0.05° and a diameter ofabout 8 cm, was placed in a MOCVD reactor for growing thin film.

The InP substrate 2′ was surface-treated by elevating a temperature inthe reactor to 660° C. and feeding a PH₃ gas. InP layer 3′ having athickness of 1 μm was grown on the InP substrate 2′ using TMIn as a rawmaterial. Then the PH₃ gas was changed for an AsH₃ gas, an InGaAs layer4′ having a thickness of 3 μm and indium content of 0.53 was grown underconditions of

-   -   raw material: TMIn and TEGa,    -   ratio of V/        : 63.4,    -   growth temperature: 660-700° C., and    -   growth rate: 1 μm/h.        The AsH₃ gas was changed for the PH₃ gas, an InP layer 5′ having        a thickness of 1 μm was grown. On growth temperature within the        above range, the operations were repeated to obtain several        epitaxial substrates.

Concave defect densities on the surfaces (of the InP layers 5′) of theepitaxial substrates were shown in FIG. 7. The concave defect densitieswere measured by using a surface defect analyzer(Surfscan 6220).

Test Example 2

An epitaxial substrate was obtained by the same operation as in Testexample 1 except that the conditions for growing the InGaAs layer 4 waschanged for the following.

-   -   ratio of V/        : 63.4,    -   growth temperature: 650° C., and    -   growth rate: 0.5-3 μm/h.        On growth rate within the above range, the operations were        repeated to obtain several epitaxial substrates. Concave defect        densities on the surfaces of the epitaxial substrates were shown        in FIG. 8.

Test Example 3

An epitaxial substrate was obtained by the same operation as in Testexample 1 except that the conditions for growing the InGaAs layer 4 waschanged for the following.

-   -   ratio of V/        : 30-112,    -   growth temperature: 650° C., and    -   growth rate: 1 μm/h.        On rate of V/        within the above range, the operations were repeated to obtain        several epitaxial substrates. Concave defect densities on the        surfaces of the epitaxial substrates were shown in FIG. 9.

1. A method for manufacturing a compound semiconductor epitaxialsubstrate comprising a step of epitaxially growing an InGaAs layer on anInP single crystal substrate or on an epitaxial layer lattice-matched tothe InP single crystal substrate under conditions of ratio of V/

: 10-100, growth temperature: 630° C.-700° C., and growth rate: 0.6μm/h-2 μm/h.
 2. The method according to claim 1, wherein the InP singlecrystal substrate has a plane direction accuracy of ±0.05° in the (100).3. The method according to claim 1, wherein the epitaxially growing iscarried out by using metal-organic chemical vapor deposition (MOCVD). 4.The method according to claim 1, wherein the epitaxially growing of theInGaAs layer includes use of gallium raw material selected from thegroup consisting of trimethyl gallium and triethyl gallium.
 5. Themethod according to claim 1, wherein the epitaxial growing of the InGaAslayer includes use of indium raw material comprising trimethyl indium.6. The method according to claim 1, wherein the epitaxial growing of theInGaAs layer includes use of arsenic raw material comprising arsine. 7.A method for reducing concave defects in a compound semiconductorepitaxial substrate comprising a step of epitaxially growing an InGaAslayer on an InP single crystal substrate or on an epitaxial layerlattice-matched to the InP single-crystal substrate under conditions ofratio of V/

: 10 to 100, growth temperature: 630° C.-700° C., and growth rate: 0.6μm/h-2 μm/h.
 8. A compound semiconductor epitaxial substrate obtained byusing the method according to claim 1.